Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 221715 AAB

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1215 PM CDT Sun Oct 22 2017

Updated for 18Z aviation discussion


18Z TAF discussion:
Variable ceilings between IFR and MVFR will exist at all TAF sites
through the majority of the period. As a cold front moves through
the area, southerly winds will switch to northwest followed by a
gradual rise in ceilings. After sunrise Monday, winds will
increase to around 10 knots with gusts approaching 20 knots by
the end of the period./26/


Squall line has diminished with leftover cold pool boundary
racing east-southeast at the moment across southern MS. While some
moderate to heavy downpours still exist in the convective cluster
over southeast MS, for the most part only light to moderate
showers remain along and behind the cold pool boundary. A narrow
tongue of mid 60s dewpoints continue to exist just ahead of the
boundary, but it looks as if it will be overtaken as slightly
cooler/more stable air remains wedged in over the southeast and
airmass will not have time to recover before cold pool boundary
arrives from the west. Made some changes to temps for this
afternoon, otherwise, did not make much change to the weather as
showers will continue with the occasional clap of thunder./26/

Prior discussion below:

Today and Tonight...High pressure at the surface and aloft continue
to breakdown across the Lower Mississippi River Valley this morning,
in response to a fast moving mid/upper trough swinging east through
the nation`s mid-section.  This trough has caused a strong cold
front to develop, which is now likewise shifting east out of the
plains and toward the ArkLaMiss.  Ahead of the front, a squall line
of showers and thunderstorms is racing southeast across West
Arkansas and Northeast Texas towards the forecast area.

Meanwhile, a little closer to home, strong moisture advection at the
surface and in the lower levels of the atmosphere, has resulted in
moderate to heavy convection rooting itself just south of the CWA,
and west of Interstate 55 along the Mississippi Louisiana state
line. This has resulted in a near steady stream of mainly light
stratiform rain lifting northward along the Interstate 55 corridor
into Central Mississippi overnight.  With the approaching squall
line from the west and the overall increasing ascent from the
aforementioned mid/upper trough moving into the region during the
morning, this activity is expected to continue to gradually lift
northeast into mainly south central and southeastern portions of the
forecast area this morning.

The squall line currently looks to move into the Delta region around
6 AM today, while undergoing a weakening trend into the process as
it`ll be entering the CWA during the diurnal minimum of the day.
Still, the heaviest of the convection will be along the leading edge
of the line, with more moderate to light rain and an occasional
rumble of thunder or two, to follow for several hours after the
initial push of this line.  While some slowing of this squall line
is possible as it continues it`s trek southeastward, it looks reach
along the Interstate 55 corridor between 8 and 10 AM, and then
reaching East Central and Southeast Mississippi between noon and 2

It`ll be across portions of South Central and Southeast Mississippi
today, where the better conglomeration of deep wind shear and
instability will reside.  Thus, a "Marginal" risk for severe weather
exists across these areas today.  There, an isolated severe storm
will be possible.  The most intense storms could produce damaging
wind gusts, and to a lesser extent hail to the size of quarters,
with a tornado not able to be ruled out.  The threat of such
activity will quickly come to an end, once the leading edge
of the squall line pushes through the area.

In addition, with a deeply moist airmass over the forecast area,
precipitable H2O values around 2+ inches, heavy rain is likely to
occur with today`s activity.  Twenty-four hour rainfall totals over
the area with this event, currently look to range in the 1-3 inch
range. Fortunately, much of the CWA has remained fairly dry since
Hurricane Nate affected the area.  Therefore, overall soil
conditions aren`t conducive for widespread flash flooding.  However,
if multiple rounds of convection train across the same locales, or
if convection becomes slow-moving over an area, flash flooding could
become possible.

Overall, rainfall looks to come to an end in the wake of the frontal
passage later this afternoon and overnight night.  Behind the front,
skies will gradually clear and winds will become northwesterly as
cold high pressure to the northwest begins building into the
forecast area.  This will result in a noticeable cool down over
the CWA as the begin the new work week. /19/

Monday through Saturday...We will start with a nearly cutoff low
pivoting across the region during the day Monday as the last of
the rains exit east of the region by early Monday. Another upper
trough will dig into the region on Tuesday as more fall like
temperatures come across the region. Highs will be in the middle
60s to the lower 70s for early in the week with lows dipping down
to the upper 30s to middle 40s by early Wednesday. The upper
trough will exit to the east at midweek as flat upper ridging
develops from the west. Temperatures will begin to moderate on
Thursday and Friday with highs in the lower to middle 70s. Lows
will moderate from the upper 40s to the middle 50s.

As we go into Friday into Saturday a cold front will approach the
region and push through by Friday night per GFS and Saturday night
per the Euro. Showers and thunderstorms will develop across the
region on Friday into Friday night and will continue through
Saturday. Have opted to go with a blend of the Euro and GFS
solutions. Do not see any organized severe weather at this time.
More fall like temperatures will come across the region with highs
in the upper 50s to upper 60s on Saturday. Lows will dip into the
middle 30s to the lower 40s. /17/


Jackson       74  55  71  51 /  83  49  10   7
Meridian      74  60  73  50 /  96  92  13   6
Vicksburg     72  53  73  50 /  89  28   8   6
Hattiesburg   76  60  73  51 /  97  72  12   5
Natchez       71  53  71  52 /  90  19   8   6
Greenville    70  52  73  49 /  91  25   8   6
Greenwood     73  54  71  48 /  92  60  10   7




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